There is a boy that is 20 - 22 years old and you are only 16 years old and he want to have sex and but you are a virgin and you don't know if you are ready what should you do?

You say no. Whether you are a virgin or not, never have sex unless you want to. Your NO is valid until the very last second and if he does not listen to you it's rape and he has no excuses. And if you also is under the age of consent in your state, it would be illegal. He is quite a bit older than you so maybe you two is not a match. If he really cares he will have no problem waiting, if he does have a problem with it there's a big risk he's only after having sex with a young girl or a virgin. Those are the immature kind of men we want to stay away from. They are also the ones who would brag to their friends about it and not respect you.